rxrpc: Fix terminal retransmission connection ID to include the channel

When retransmitting the final ACK or ABORT packet for a call, the cid field
in the packet header is set to the connection's cid, but this is incorrect
as it also needs to include the channel number on that connection that the
call was made on.

Fix this by OR'ing in the channel number.

Note that this fixes the bug that:

	commit 1a025028
	rxrpc: Fix handling of call quietly cancelled out on server

works around.  I'm not intending to revert that as it will help protect
against problems that might occur on the server.

Fixes: 3136ef49 ("rxrpc: Delay terminal ACK transmission on a client call")
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>